The subject matter disclosed herein relates to rotor blades. More specifically, the subject disclosure relates to multi-element airfoil rotor blades.
Multi-element airfoils are commonly used on fixed wing aircraft, and are commonly incorporated as leading edge or trailing edge slats. The slats are extended or articulated under certain flight conditions, such as high angle of attack and low Mach number, and are typically retracted under other conditions.
Multi-element airfoils are known in rotors of rotary-winged aircraft. Slats, which are located at a rotor blade leading edge, similar to those utilized on fixed wings, increase the maximum lift coefficient of the rotor blade, when compared to a rotor blade without slats. Increased maximum lift coefficient enables the rotor to achieve greater thrust and/or increased flight speeds. Such improvements favorably impact the payload/ range capabilities and maneuverability, and reduce rotor tip speeds leading to a reduction in noise signatures for the rotary-winged aircraft.
Struts connecting these slats to the main portion of the rotor blade, however, must typically be designed to withstand both the lifting forces on the slats and centrifugal forces generated by the rotation of the rotor about its axis. The resulting struts generate high levels of parasitic drag, which reduces the beneficial effects of the slats.